Optical Drive, These are used for burning cd's or dvd's. They can also be used for uploading information onto your hard drive. 52x is the fastest a cd can be burned and read, as for a dvd the fastest it can be burned is 16x and also read at 16x
Motherboard, ,also known as a mainboard, logic board, or system board, and sometimes abbreviated as mobo, is the central or primary circuit board making up a complex electronic system, such as a computer.
Heatsink/fan. You always have to have one of these ontop of your processor or it will get to hot and fry. If your heatsink/fan were to ever fail turn off the computer right away.